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Technical PtII-Ratio of Spring weight to unsprung weight unfavorable, what helps?

Discussion in 'The Hokey Ass Message Board' started by 31Vicky with a hemi, Apr 27, 2014.

  1. TANNERGANG
    Joined: Jan 18, 2011
    Posts: 1,278

    TANNERGANG
    Member
    from alabama

    All this work and theories to prove an old mans simple little motor mount wrong.....I love it...while you all have spent countless hours arguing I've put about 300 miles of evening ride time on my '32....."Ain't America a Great Place to Live"
     
  2. Cowtown Speed Shop
    Joined: Sep 26, 2010
    Posts: 1,185

    Cowtown Speed Shop
    Member
    from KC

    You are not to scale here, there is alot of calculating to do, But get a longer beam from the weight and bolt it as far to the left of the top beam as you can.
     
  3. y-oh-y
    Joined: Feb 14, 2012
    Posts: 116

    y-oh-y
    Member

    If weight is where it is, how do my load levelers on my truck/trailer work ? They do a real good job getting my front end back down without adding any more weight.

    I can see where a rear facing mounting bar would transfer some engine weight to the rear wheels.

    Really enjoying this thread, got my simple mind a spinning.
     
  4. Can we agree..,
    • That the law of conservation of energy" stands true & to date has not been broken
    •A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque.
    • that 800lbs of weight applied to a 12" bar would generate 800 ( lb ft) of torque

    Is all that true & agreeable ? Any arguments to the contrary ?

    I'm more than reasonably certain that it is agreeable and there are no arguments thus far.

    So lets agree on some more things ...

    •The expression ( Lb feet) has been abbreviated from "pounds of force per feet" , so torque is a force, a force of rotation.

    • If a force is allowed to act through a distance, it is doing mechanical work. Similarly, if torque is allowed to act through a rotational distance, it is doing work.

    • mechanical work is an exchange of energy.

    • energy is never lost

    Is that true and agreeable and free of controversy?
    Again I'm more than reasonably certain that this is so.

    Ok let's agree on some more things.

    • if torque or another force is applied to anything, there is a reaction.

    • if torque is applied to a car chassis it reacts.

    • Redirecting the connections of this torque changes the reaction out come.

    Agreeable ? I believe so but everyone might not know how to get the car to do what you want, some may get lost.

    Lets agree on some more stuff.
    • If we were to hang an 800 lb engine off motor mount in such a way as to create a rotational force at the mounts coupling it is doing mechanical work upon that mount to frame coupling. This work is transfered into the frame.

    Since its static and not changing angular vector it's not called torque anymore its called a "moment" ( engineering term that looses me all the time)

    Agreeable ? I believe so.

    Now where did this "work" and exchange of energy go as it transfers into the frame rails ?
    What does it do? It's got to do something
     
  5. saltflats
    Joined: Aug 14, 2007
    Posts: 11,075

    saltflats
    Member
    from Missouri

    Hay Tanner I think I remember some racing classes would not let you run anything other than stock mounts and brackets or maybe I just dreamed it. So could be something to your idea.
     
  6. blowby
    Joined: Dec 27, 2012
    Posts: 8,063

    blowby
    Member
    from Nicasio Ca

    Still no answer to post 147. Let me say it another way. You walk up to chassis with mount #2. You read the scales, front and rear. Then you gently lay a brace across, as in #3. You bolt this brace in place. There is no longer any "leverage" from the other leg. Have the scales changed because you bolted the brace in?

    [​IMG]
     
  7. moving the fulcrum would change the load. does moving the motor mount do this? and where is the fulcrum?
     
  8. Maybe put some details In there such as the direction of force.
    As its drawn I see vertical poles. As its drawn if a weight were hung from there enough to bend it. 1 would bend at the connection. 2 would bend further down at its connection. 3 would be much harder to bend only if the ends were fixed.

    If I look at your pictures and assume the weight/ force is in a direction of "from my eyes to the back of the page- the weight will want to rotate the rail in that same direction of the force. If the rail were fixed so that it couldn't rotate, the smooth side would be lighter and the side with the mount would be heavier instead of evenly distributed. If that were a tube, one side would be in compression and the other in tension. If enough weight to bend/ brake it were applied, 1 would break at its connection, to would break further down at its connection and 3 would withstand much more because it has 2 connections to break.

    If I were to apply the force from the left and wanting to go right,
    With enough force to bend it the rail 1 would bend evenly at the mount. Like a v with the mount in the center.
    2 would be interesting, as I see the long end fighting to go left as the force goes right.
     
  9. blowby
    Joined: Dec 27, 2012
    Posts: 8,063

    blowby
    Member
    from Nicasio Ca

    Sorry, I'm still picturing the drawing that started this discussion. Think of it as a frame rail same as Tanner's post #18

    [​IMG]
     
    Last edited: Apr 30, 2014
  10. I'm not sure where the fulcrum is.

    Picture torquing head bolts with the engine on a stand or mounted in a car.
    The bolt turns and all stays put while the bolt gets tighter.

    Now put the engine on the floor and try to torqu the bolts. You'll chance that engine all over the shop, that work is going some where right? Where's the fulcrum there? I don't think there is a stationary fulcrum that's why the entire engine moves.

    Imagine an I beam on the bench,
    You want bolt a plate on the end of it to 800 ft lbs.
    pushing down on the wrench with 800 lbs is going to flip the end up or at least make it lighter. Where's the fulcrum when that happens?

    I'm thinking the fulcrum moves around to the point where things are experiencing the most stress within the member. There a term for non stationary fulcrums but I can't remember.
     
  11. blowby
    Joined: Dec 27, 2012
    Posts: 8,063

    blowby
    Member
    from Nicasio Ca

    Why didn't you mention that here?:

    I maintain that if the theory were true there would be a resulting change in weight distribution regardless of the lengths and weights involved. But I'm not going to test a full size mockup, and I'm sure you are'nt either so we'll have to agree to disagree.
     
  12. Littleman
    Joined: Aug 25, 2004
    Posts: 2,619

    Littleman
    Alliance Member
    from OHIO, USA

    A vehicle sitting on scales is one thing.........That same vehicle launching during that last yellow bulb drop is something else......Follow the energy from the action of mashing the fun pedal to the reaction of that energy flow thru the chassis to plant the rear wheels.........My new engine mounts are actually like # 3 above.....I supported it w/ the leg going back.......I played w/ my CG with locations I chose before hand ect..........I enjoy thinking about some of this stuff......As for a street vehicle..........not much advantage diving deep into this........set it up for a good balance for driving the streets and dial in the shocks, springs and leafs.....whatever you have.......
     

  13. I see a torque load situation being created.
    The torque force is being transferred to the rail right at the connection.
    Its got to be doing something.

    I'm unsure of what it's doing but " it does nothing" is not correct.

    Just picture this.
    Take the rail off the car and put it on the bench wide side down.
    Place 4 dial indicators , 2 at the front end and two at the back.
    No try to spin the rail on the table, you will move 2 indicators to their max and 2 to there minimum. One of each at the front and one of each at the rear.

    Pretty easy to see if my explanation didnt loose you.

    Ok now Change the dial indicators to lateral scales and pre-load them so the all read 100 lbs.
    Go about where the motor mount would be and attach a torque wrench now give her some pull, at the front, one scale will read more that 100 and the other less. On the rear end those two scales will read opposite if you are trying to spin the rail like a compass needle
     
  14. Patman187
    Joined: Dec 7, 2008
    Posts: 122

    Patman187
    Member
    from Nebraska

    Not trying to be antagonistic or crappy but the load is different....

    DSC02372.jpg

    DSC02373.jpg

    DSC02370.jpg

    DSC02371.jpg

    Now imagine with one inch of chassis lift at the front how much difference that will make on the rear tire load more load= less noticeable unsprung weight because the unsprung weight has to over come more weight than before with stock type engine mount. TANNERGANG is right now come back TANNERGANG, this is the long way around but the whole idea is for more load to for lack of a better word neutralize some unsprung weight.

    Pat
     
  15. That's not crappy or antagonistic
     
  16. Patman187
    Joined: Dec 7, 2008
    Posts: 122

    Patman187
    Member
    from Nebraska

    Through my personal experience with open wheel dirt cars this is common knowledge but not so obvious because the whole chassis is fabricated tubing and it all looks a little funny. Usually the way a midget or sprint car is built and set up this effect is very important for forward bite but the unload rate is what is scary in a midget or sprint car. The next time you go to a open wheel race watch when a driver goes from full throttle to none the chassis is rared up and then plops back down and the car wiggles around this is the extreme end of it TANNERGANG knows what happens in a more normal car I hope he comes back to this .

    Pat
     
  17. Ulu
    Joined: Feb 26, 2014
    Posts: 1,773

    Ulu
    Member
    from CenCal

    I think you guys are confusing static and dynamic responses. They don't mix with simple math.

    And the test with the screwdriver appears to show a static explanation for something that is really only apparent dynamically.

    So while Tannergang's engine mount does zero statically, dynamically it could be quite effective, because it changes the effective stiffness of the frame. The frame doesn't get stiffer. The loci of applied forces simply makes it respond differently in resisting the forces.

    When you launch, the suspension and frame all twist, and just how they twist can affect effective traction dramatically.

    Doing what tanner did changed the relative stiffness, and therefore relative dynamic responses, of the front frame vs the rear frame.
     
  18. blowby
    Joined: Dec 27, 2012
    Posts: 8,063

    blowby
    Member
    from Nicasio Ca


    Makes sense. I would equate having a smooth ride in a street car in regards to unsprung weight not as launching from the green light, or loading and unloading in a dirt tracker, but more towards the static end - going down the road neither on nor off the gas and hitting a bump.
     
  19. Judd
    Joined: Feb 26, 2003
    Posts: 1,894

    Judd
    Member

    I'll second this, disc brakes are mounted on center section ( sprung ) so only axles hubs wheels tires and part of shocks are unsprung.

     
  20. Patman187
    Joined: Dec 7, 2008
    Posts: 122

    Patman187
    Member
    from Nebraska

    Ulu That is the idea and I think that is why some guys with higher math and engineering skill are having a hard time with this, I understand where they are coming from some good examples have been given to show this doesn't work. But this is a very useful thing to think about when setting up a car because you have to make engine mounts anyway right? I competed with many factory chassis builders and the light came on for me one night pitted next to one, I saw the crew change the motor plate bolt locations they put the motor plate bolts way up high in the chassis the engine did not move up or back stayed the same just the bolt location in the feature they went to the bottom of the track and I don't think the left front ever touched the ground winged down dragging the left rear frame rail. It simply changed where the torque was applied to the chassis to make it behave differently now lets think why the production cars moved the mounts from the front of the engine to the middle of the block.

    Pat
     
  21. LBH
    Joined: Dec 22, 2010
    Posts: 66

    LBH
    Member

    Moving the motor plate bolts up in the chassis effectively made the the wrench longer which multiplied the torque's effect on the frame ...... this similar to if the mount looked like this \ which changed the length of the mount as well as its mounting location on the frame ........... by doing either example you have multiplied the load on the frame.... and therefore the handling ......tp
     
  22. Ulu
    Joined: Feb 26, 2014
    Posts: 1,773

    Ulu
    Member
    from CenCal

    I think It also slowed the axial rotation (parallel to the white line) of the front end, as the wheels came up, because the rotational inertia was greater when the engine mount was moved up.

    Making the chassis twist slower might sometimes be as good as making it twist less, 'cause you don't add steel (weight!) making it stiffer. You delay the twist so it doesn't unsettle your hookup & make you burn the tires.
     
  23. So this is starting to turn around now ?
    We went from makes no fucking difference
    To
    Might do something, maybe but I doubt it
    To
    Does something
    To
    maybe it does this or maybe it does that.

    Major accomplishment :)
     
  24. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    We might be getting a little off track as this thread was originally about sprung unsprung weights and how their ratios may effect ride quality, not how a chassis reacts to torque applied. Also might be misdirecting good logic a bit as the points now being discussed by Vicky and others do have an effect but other than a slight structural weight difference its mostly converted into added stress.

    By repositioning the motor mount leg at the frame you are adding/changing torque to the frame but also in an equal amount cancelling it out by the frame with it's "lever" becoming longer from moving to the new mounting point.

    I hope nobody thinks I'm attacking them. More just have a bit of difficulty strolling by a good technical discussion that I feel strongly about.
     
    Last edited: Apr 30, 2014
  25. Ulu
    Joined: Feb 26, 2014
    Posts: 1,773

    Ulu
    Member
    from CenCal

    It might cancel in static calculation, depending.

    Figure in flex and motion & it doesn't.

    Some gets lost in that internal stress.

    Some gets lost in mechanical inefficiencies.
    (Even the simplest machines have them.)

    Things never cancel perfectly & for the same reasons that you can't have perpetual motion.
     
  26. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    Sorry was just referring to how weight is effected which I still believe is nil. Also corrected my to to do.
     
  27. studedudeus
    Joined: Jun 11, 2008
    Posts: 141

    studedudeus
    Member

    Vicky,

    Kind of a recap of the posts that are relevant to your situation, so we're all on the same page.

    All this physics is interesting, but not really relevant for the vehicle you are talking about. You seem to be talking about improving how the vehicle you described rides.

    The simple explaination is; "Un-sprung" weight is everything attached to the axle, while "sprung" weight is everything attached to the frame.

    Unsprung can be reduced by using lighter wheels, tires, brakes and axles. Attaching Anti-sway bars to the frame (sprung) with only the link and end of the bar being attached to the axle (unsprung). Shocks are the same way, heavy part attached to the frame, and the rod attached to the axle.

    Now the Sprung/Unsprung ratio can be increased by making unsprung lighter or by making sprung heavier. You've stated that unsprung has already been lowered as much as possible without going to really exotic/expensive stuff. Increasing sprung weight is always undesirable in either the Hot Rod or Racing worlds. However, the ratio can also be affected by how the weight is distributed along the frame. The weight can be moved along the frame, by moving the engine back. Or by extending the frame forward of the motor. Moving batteries, and other heavy objects out of the engine compartment and back into the trunk also helps. Obviously these have limits.

    So assuming the weights that you have are set, you next have to look at how it rides. Since old hot rods like this are typically light in back, you want to use lower spring rates in back, and not too firm of shocks. In order to maintain ride height, you have to be able to support the weight of the vehicle over the axle. This is done by combining spring rate and spring pre-load.

    Leaf spring rates are determined by thickness of leaves and number of leaves. So you'll have to determine how to lower the spring rate. Then you use arch and mounting bracket positions to get the ride height you want. I seriously doubt that you'ld need progressive spring rates. You just want a rate that is low enough that the body doesn't get kicked around by every bump that moves the axle. :Likewise, shocks should be as light as possible. They need to damp out the movement of the spring, but not increase the spring rate. So gas shocks many not be the answer here.

    Hope this helps.
     
  28. Well, it was brought up by tanner as a weight shift mechanism to effectively increase the sprung weight applied over the rear and that would change the sprung vs unsprung ratio. Maybe so, maybe not, maybe not literally and physically but if it causes a reaction that's equivalent to a physical weight shift then it can not be discounted.

    If you are adding torque (i believe torque force is actually called some other type of force because it is static in this case) to anything - something will change and that much is for certain. Lots of these posts say there is no difference, nothing changes, and claims of " lack of understanding.

    I'd like to comment on another point you made. "It's mostly converted to added stress" . There's no free ride with anything and the energy applied from a suspended weight will have a cost. Part of the cost is added stress because of the extra work being exerted into the chassis. If the chassis is being forced to work like something it's really not, then the cost vs benefit analysis needs to be weighed.

    We still haven't come to a solid conclusion of what it actually does or how it does it, but there's been a quantum leap from "it does nothing" to "yes, something is going on". Can this benefit our car building? Well anything that makes you think cultivates the mind and you'll be better for that. If you are better you'll be better at what ever you are doing. So yeah it's going to help build better cars.
     
  29. changing mounting points would change the torsional stiffness. it's a crutch softest suspension is the best way to go but a lot of racers like flexible frames it's easier to set-up
    if you can't move or remove weight work on weight transfer.
     
  30. Littleman
    Joined: Aug 25, 2004
    Posts: 2,619

    Littleman
    Alliance Member
    from OHIO, USA

    If you scale the vehicle and position the engine per your desired use of the vehicle along w/ all the other systems that need to get along w/ one another. You will not need to build a mount like that..unless you are in the grey area of an engine location rule and limited.

    I do think that mount properly supported will transfer the energy thru it and affect the chassis in a positive way depending on your use..I understood the engine mount idea from the start, but I was visualizing the energy travel ...be it right or wrong. I am not that much of a charts and graph kinda guy........

    I also think you can out engineer yourself if not careful..........I 've attended plenty of engineering meeting w/ killer presentations, charts and colored graphs......and at the same time they all seemed to check in their common sense at the door prior to entering..I mention something stupid simple and the lights go on.....

    This is good stuff..constructive conversation is alway's healthy, being combative while wearing blinders....you will never learn and or get better..some listen to learn..others think they know it all...When building a hotrod.....everything should be on a diet..ha ha ha..light is faster as I mention before.......Littleman Dave
     

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